1. Field of the Invention
This invention relates to an improvement to a rotary damper to make it operate as a shock absorber and act on a turning body such as a door or a toilet lid when the latter is falling down to the closed position.
2. Description of Related Background Art
Japanese Utility Model Laid-Open No. 62-81739 discloses a rotary damper of the type under consideration as shown in FIGS. 7A and 7B of the accompanying drawings.
Referring to FIGS. 7A and 7B, which illustrate an embodiment of a rotary damper according to the above document and adapted to be used for the keyboard lid of a piano. The rotary damper A is linked to the keyboard lid b by way of a join d so that the keyboard lid b may be closed smoothly at an appropriate moving speed without emitting a large bumping sound and/or vibrating violently when it gets to the final closed position.
As seen from FIG. 7B, the rotary damper A comprises a casing e, a movable shaft h loosely fitted into the inner cavity g of the casing e as defined by the inner peripheral surface f thereof with a shaft end i protecting from opening j of the casing e, a pair of O-rings k1 and k2 fitted into the movable shaft h and pressed against the inner peripheral surface f of the casing e so that the gap between the inner peripheral surface f of the casing e and the movable shaft h is hermetically sealed and viscous fluid m is watertightly contained in the gap and a torsion spring p having anchoring ends q1 and q2 secured respectively to projecting section I of the movable shaft h and closure section r of the casing e.
With the above described known rotary damper A, the viscous shearing resistance generated in the viscous fluid watertightly contained in the gap between the inner peripheral surface f of the casing e and the movable shaft h that is typically polymeric viscous fluid such as polyisobutyne or the like as a result of a rotary motion of the cylindrical shaft h is utilized as a damping force.
Thus, the rotary damper A as described above is accompanied by a number of drawbacks including that it cannot provide a sufficient and satisfactory damping effect when the viscous shearing resistance is used as a sole source of damping power, that it requires a high level of machining precision because the torque of the damper changes from the expected value if the size of the gap varies from the designed value, that the components including the casing e, the movable shaft h, the O-rings k1, k2 and the viscous fluid m are large in number and costly and that, while the torque of the damper effectively operates when the keyboard lid b is closed, a substantially same viscous shearing resistance appears also when the keyboard lid b is opened.
In view of the above identified problems of the prior art, it is therefore the object of the present invention to provide a rotary damper comprising only a casing and a movable shaft having a cylindrical shaft section that includes an arched non-resilient section and an eccentric resilient section extending peripherally outwardly from the arched non-resilient section to show a diametrical size greater than that of the inner peripheral surface of the casing so that the outer peripheral surface of the eccentric resilient section may resiliently slide on the inner peripheral surface of the casing.
With such an arrangement, torque is generated in the damper due to the considerably large frictional force that arises between the inner peripheral surface of the casing and the eccentric resilient section when the movable shaft is driven to rotate toward the free end of the eccentric resilient section, whereas the frictional force can be reduced greatly without providing the viscous fluid with a specific flow path unlike the prior art that utilizes the viscous shearing resistance of the viscous fluid when the movable shaft is subjected to a rotary force trying to rotate it in the opposite sense. Thus, a large torque can be obtained in the damper principally comprising only two components without requiring an enhanced level of machining precision.
The above object is achieved by providing a rotary damper comprising a casing and a movable shaft having a cylindrical shaft section loosely, freely rotatably and unreleasably fitted into the inner cavity of the casing as defined by the inner peripheral surface thereof and a shaft end section linked to the cylindrical shaft section and projecting from the opening of the casing, said cylindrical shaft section of the movable shaft including an arcuate non-resilient section extending from a peripheral edge thereof to an axial base line close to the other free peripheral edge thereof and an eccentric resilient section extending from said axial base line to the other free peripheral edge thereof with its eccentricity increasing as a function of the distance from said base line relative to the radius of curvature of the inner peripheral surface so as to resiliently abut the inner peripheral surface.
The above object can be achieved highly reliably when the eccentric resilient section is formed by cutting the cylindrical shaft section of the movable shaft to produce an axial slit and a radial sit perpendicular to said axial slit that defines the eccentric resilient section extending from the arcuate non-resilient section.
Thus, there is provided a rotary damper comprising a casing and a movable shaft having a loose cylindrical shaft section freely rotatably and unreleasably fitted into the inner cavity of the casing as defined by the inner peripheral surface thereof and a shaft end section linked to the cylindrical shaft section and projecting from the opening of the casing, said cylindrical shaft section of the movable shaft including an arcuate non-resilient section extending from a peripheral edge thereof to an axial base line close to the other free peripheral edge thereof and formed by cutting the cylindrical shaft section from the closure side to produce an axial slit defining said peripheral edge and the other free peripheral edge and then from the end of said axial slit located close to the shaft end section perpendicularly relative to said axial slit to produce a radial slit and an eccentric resilient section extending from said axial base line to the other free peripheral edge thereof with its eccentricity increasing as a function of the distance from said base line relative to the radius of curvature of the inner peripheral surface so as to resiliently abut the inner peripheral surface.
Preferably, viscous fluid is watertightly sealed in the cavity of the casing including the gap between the inner peripheral surface of the casing and the eccentric resilient section by using a sealing O-ring so that not only the damping effect of the torque of the damper generated by said eccentric resilient section is boosted by the shearing resistance of the viscous fluid sealed in the cavity but also the viscous fluid operates as a lubricant to make the movable shaft rotate smoothly and increase the durability of the rotary damper.
Thus, in a rotary damper, viscous fluid is watertightly contained in the cavity of said casing by means of a sealing O-ring arranged between the shaft end section of the movable shaft and the inner peripheral surface of the casing.
Preferably, the volume of the viscous fluid contained in the cavity of the casing is reduced and, at the same time, the torque of the damper is increased by the viscous fluid contained in the cavity of the casing to provide to a sufficiently large viscous shearing resistance and a damping effect greater than the one obtained by the arrangement where an axial rod having a diameter slightly smaller than that of the cylindrical space defined by the inner peripheral surface of the cylindrical shaft section of the movable shaft is made to project from the closure of the casing.
Thus, in a rotary damper, an axial rod having a diameter slightly smaller than that of the cylindrical space defined by the inner peripheral surface of the cylindrical shaft section of the movable shaft is provided and projecting from the closure of the casing.
Preferably, a sufficiently large damping effect is obtained and, if the lid to be used with the rotary damper is very heavy, it can be dosed slowly and opened with ease by the resilient force of a spring when a torsion bar spring or a coil spring is contained in the cavity of the casing in addition to the movable shaft having the eccentric resilient section and the opposite ends of the spring are securely held to the movable shaft and the casing respectively so that the torque of the torsion bar spring or the coil spring is added to the torque of the damper due to the resilient force of the eccentric resilient section.
Thus, in a rotary damper, a torsion bar spring or a coil spring is contained in the cavity of the casing and the opposite ends of the spring are securely held respectively to the casing and the movable shaft.
Still preferably, not only viscous fluid is watertightly sealed in the cavity of the casing and the eccentric resilient section but also a torsion bar spring or a coil spring is contained in the cavity to exploit both the viscous shearing resistance of the viscous fluid and the resiliency of the spring to boost the torque of the damper.
Thus, in a rotary damper, viscous fluid is watertightly contained in the cavity of said casing by means of a sealing O-ring arranged between the shaft end section of the movable shaft and the inner peripheral surface of the casing and a torsion bar spring or a coil spring is contained in the cavity with the opposite ends of the spring securely held respectively to the casing and the movable shaft.
Still preferably, in additional to the use of an eccentric resilient section and a torsion bar spring or a coil spring, said other free peripheral edge is constantly urged outwardly to press the inner peripheral surface of the casing by rigidly securing an end of the spring to the casing and inserting the other end between said peripheral edge and said other free peripheral edge of the cylindrical shaft section of said movable shaft so as to make it resiliently abut and exert the effect of the spring onto said other free peripheral edge in order to avoid a situation where the eccentric resilient section is crept to reduce the pressure of the eccentric resilient section against the inner peripheral surface. Then, any reduction with time of the resiliency of the eccentric resilient section and hence that of the torque of the damper can be prevented from taking place.
Thus, in a rotary damper, a torsion bar spring or a coil spring is contained in the cavity of the casing with an end thereof securely held to the casing and the other end inserted between said peripheral edge and said other free peripheral edge of the cylindrical shaft section of said movable shaft so as to make it resiliently abut said other free peripheral edge.
Still preferably, the eccentric resilient section is prevented from being crept to prevent any reduction with time of the resiliency of the eccentric resilient section and hence that of the torque of the damper from taking place even when no spring is used to urge the eccentric resilient section to press the inner peripheral surface of the casing.
Thus, in a rotary damper, a resilient member is inserted between said peripheral edge and said other free peripheral edge of the cylindrical shaft section of said movable shaft to urge said eccentric resilient section so as to press the inner peripheral surface of the casing.
Still preferably, the torque of the damper can reliably be provided to a large extent by the eccentric resilient section without using any additional member simply by arranging a projection in the casing.
Thus in a rotary damper, a notch is formed in said arcuate non-resilient section from said peripheral edge of said cylindrical shaft section to make it open to said axial slit and an inner projection is formed on the inner peripheral surface of said casing with its height increasing in the sense of extension of said eccentric resilient section and adapted to be received in said notch so as to make said eccentric resilient section of said movable shaft to be resiliently urged toward the center of the cavity when laid on said inner projection by the rotary motion of the movable shaft.